4 Search Results for "Carmeli, Nofar"

Document
DOI: 10.4230/LIPIcs.STACS.2023.18
Geometric Amortization of Enumeration Algorithms

Authors: Florent Capelli and Yann Strozecki

Published in: LIPIcs, Volume 254, 40th International Symposium on Theoretical Aspects of Computer Science (STACS 2023)

Abstract
In this paper, we introduce a technique we call geometric amortization for enumeration algorithms, which can be used to make the delay of enumeration algorithms more regular with little overhead on the space it uses. More precisely, we consider enumeration algorithms having incremental linear delay, that is, algorithms enumerating, on input x, a set A(x) such that for every t ≤ ♯ A(x), it outputs at least t solutions in time O(t⋅p(|x|)), where p is a polynomial. We call p the incremental delay of the algorithm. While it is folklore that one can transform such an algorithm into an algorithm with maximal delay O(p(|x|)), the naive transformation may use exponential space. We show that, using geometric amortization, such an algorithm can be transformed into an algorithm with delay O(p(|x|)log(♯A(x))) and space O(s log(♯A(x))) where s is the space used by the original algorithm. In terms of complexity, we prove that classes DelayP and IncP₁ with polynomial space coincide. We apply geometric amortization to show that one can trade the delay of flashlight search algorithms for their average delay up to a factor of O(log(♯A(x))). We illustrate how this tradeoff is advantageous for the enumeration of solutions of DNF formulas.
Cite as

Florent Capelli and Yann Strozecki. Geometric Amortization of Enumeration Algorithms. In 40th International Symposium on Theoretical Aspects of Computer Science (STACS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 254, pp. 18:1-18:22, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2023)

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@InProceedings{capelli_et_al:LIPIcs.STACS.2023.18,
  author =	{Capelli, Florent and Strozecki, Yann},
  title =	{{Geometric Amortization of Enumeration Algorithms}},
  booktitle =	{40th International Symposium on Theoretical Aspects of Computer Science (STACS 2023)},
  pages =	{18:1--18:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-266-2},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{254},
  editor =	{Berenbrink, Petra and Bouyer, Patricia and Dawar, Anuj and Kant\'{e}, Mamadou Moustapha},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2023.18},
  URN =		{urn:nbn:de:0030-drops-176703},
  doi =		{10.4230/LIPIcs.STACS.2023.18},
  annote =	{Keywords: Enumeration, Polynomial Delay, Incremental Delay, Amortization}
}
Document
Invited Talk
DOI: 10.4230/LIPIcs.ICDT.2022.3
Answering Unions of Conjunctive Queries with Ideal Time Guarantees (Invited Talk)

Authors: Nofar Carmeli

Published in: LIPIcs, Volume 220, 25th International Conference on Database Theory (ICDT 2022)

Abstract
The holy grail we strive for is, given a query, to identify an algorithm that answers it over general databases with optimal time guarantees for the specific query. In this tutorial, we focus on what can be seen as ideal time guarantees: linear preprocessing (needed to read the input) and constant time per answer (needed to print the output). We seek to understand which queries can be solved with these (or almost these) time guarantees and how. We start with the basic building blocks of database queries: joins, and slowly increase the expressivity by introducing projections and unions until we cover positive relational algebra. We first consider the task of enumerating all query answers and then discuss related, more demanding, tasks such as ordered enumeration and direct access to query answers. We investigate the challenges in answering such queries and provide algorithms and conditional lower bounds
Cite as

Nofar Carmeli. Answering Unions of Conjunctive Queries with Ideal Time Guarantees (Invited Talk). In 25th International Conference on Database Theory (ICDT 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 220, p. 3:1, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2022)

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@InProceedings{carmeli:LIPIcs.ICDT.2022.3,
  author =	{Carmeli, Nofar},
  title =	{{Answering Unions of Conjunctive Queries with Ideal Time Guarantees}},
  booktitle =	{25th International Conference on Database Theory (ICDT 2022)},
  pages =	{3:1--3:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-223-5},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{220},
  editor =	{Olteanu, Dan and Vortmeier, Nils},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2022.3},
  URN =		{urn:nbn:de:0030-drops-158771},
  doi =		{10.4230/LIPIcs.ICDT.2022.3},
  annote =	{Keywords: query evaluation, enumeration, fine-grained complexity, constant delay, union of conjunctive queries}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2021.16
Database Repairing with Soft Functional Dependencies

Authors: Nofar Carmeli, Martin Grohe, Benny Kimelfeld, Ester Livshits, and Muhammad Tibi

Published in: LIPIcs, Volume 186, 24th International Conference on Database Theory (ICDT 2021)

Abstract
A common interpretation of soft constraints penalizes the database for every violation of every constraint, where the penalty is the cost (weight) of the constraint. A computational challenge is that of finding an optimal subset: a collection of database tuples that minimizes the total penalty when each tuple has a cost of being excluded. When the constraints are strict (i.e., have an infinite cost), this subset is a "cardinality repair" of an inconsistent database; in soft interpretations, this subset corresponds to a "most probable world" of a probabilistic database, a "most likely intention" of a probabilistic unclean database, and so on. Within the class of functional dependencies, the complexity of finding a cardinality repair is thoroughly understood. Yet, very little is known about the complexity of finding an optimal subset for the more general soft semantics. This paper makes a significant progress in this direction. In addition to general insights about the hardness and approximability of the problem, we present algorithms for two special cases: a single functional dependency, and a bipartite matching. The latter is the problem of finding an optimal "almost matching" of a bipartite graph where a penalty is paid for every lost edge and every violation of monogamy.
Cite as

Nofar Carmeli, Martin Grohe, Benny Kimelfeld, Ester Livshits, and Muhammad Tibi. Database Repairing with Soft Functional Dependencies. In 24th International Conference on Database Theory (ICDT 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 186, pp. 16:1-16:17, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2021)

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@InProceedings{carmeli_et_al:LIPIcs.ICDT.2021.16,
  author =	{Carmeli, Nofar and Grohe, Martin and Kimelfeld, Benny and Livshits, Ester and Tibi, Muhammad},
  title =	{{Database Repairing with Soft Functional Dependencies}},
  booktitle =	{24th International Conference on Database Theory (ICDT 2021)},
  pages =	{16:1--16:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-179-5},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{186},
  editor =	{Yi, Ke and Wei, Zhewei},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2021.16},
  URN =		{urn:nbn:de:0030-drops-137245},
  doi =		{10.4230/LIPIcs.ICDT.2021.16},
  annote =	{Keywords: Database inconsistency, database repairs, integrity constraints, soft constraints, functional dependencies}
}
Document
DOI: 10.4230/LIPIcs.ICDT.2018.11
Enumeration Complexity of Conjunctive Queries with Functional Dependencies

Authors: Nofar Carmeli and Markus Kröll

Published in: LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Abstract
We study the complexity of enumerating the answers of Conjunctive Queries (CQs) in the presence of Functional Dependencies (FDs). Our focus is on the ability to list output tuples with a constant delay in between, following a linear-time preprocessing. A known dichotomy classifies the acyclic self-join-free CQs into those that admit such enumeration, and those that do not. However, this classification no longer holds in the common case where the database exhibits dependencies among attributes. That is, some queries that are classified as hard are in fact tractable if dependencies are accounted for. We establish a generalization of the dichotomy to accommodate FDs; hence, our classification determines which combination of a CQ and a set of FDs admits constant-delay enumeration with a linear-time preprocessing. In addition, we generalize a hardness result for cyclic CQs to accommodate a common type of FDs. Further conclusions of our development include a dichotomy for enumeration with linear delay, and a dichotomy for CQs with disequalities. Finally, we show that all our results apply to the known class of "cardinality dependencies" that generalize FDs (e.g., by stating an upper bound on the number of genres per movies, or friends per person).
Cite as

Nofar Carmeli and Markus Kröll. Enumeration Complexity of Conjunctive Queries with Functional Dependencies. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 11:1-11:17, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2018)

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@InProceedings{carmeli_et_al:LIPIcs.ICDT.2018.11,
  author =	{Carmeli, Nofar and Kr\"{o}ll, Markus},
  title =	{{Enumeration Complexity of Conjunctive Queries with Functional Dependencies}},
  booktitle =	{21st International Conference on Database Theory (ICDT 2018)},
  pages =	{11:1--11:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-063-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{98},
  editor =	{Kimelfeld, Benny and Amsterdamer, Yael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.11},
  URN =		{urn:nbn:de:0030-drops-85988},
  doi =		{10.4230/LIPIcs.ICDT.2018.11},
  annote =	{Keywords: Enumeration, Complexity, CQs}
}
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